1. Field of the Invention
This invention relates to polymeric compositions useful in coating applications. More specifically, this invention relates to polymer compositions having good melt flow under zero shear conditions and useful in coating various substrates such as glass bottles which are employed as containers particularly in the carbonated beverage and beer industries.
2. Description of the Prior Art
The hazards of using glass containers, particularly glass bottles which contain beer or carbonated beverages, are well known. Breakage of such bottles often takes place due to the internal pressure exerted by the pressurized gas in the carbonated beverage or beer as well as by dropping the bottles and other impacts caused by external forces which occur not only in the course of production and distribution of the bottled product, but also as a result of handling of the bottled product by consumers. Such breakage may result in injuries to the human body.
Coatings have been applied to such bottles in order to prevent scattering of the broken glass upon breakage. In this connection, see West German Patent DT2,636,157 and U.S. Pat. No. 3,823,032. The latter patent discloses that thermoplastic elastomers such as block copolymers of styrene and butadiene are useful in coating glass bottles. Thermoplastic elastomeric compositions, having improved environmental resistance, are disclosed in U.S. Pat. No. 3,686,365. These polymeric compositions comprise
(a) about 80 to 99 percent of block copolymers having at least two mono alpha alkenyl arene polymer blocks and at least one conjugated diene polymer block and PA1 (b) about 20 to 1 percent of a selectively hydrogenated block copolymer having, prior to hydrogenation, at least one mono alpha alkenyl arene polymer block and at least one conjugated diene polymer block, said block copolymer having been selectively hydrogenated to saturate at least 80 percent of the olefinic double bonds and 0 to 25 percent of the aromatic double bonds. PA1 A. a glass container PA1 B. an inner coat of a non-tacky powder composition intimately contacted on the external wall surface of the bottle, and PA1 C. an outer coat of a synthetic resin covering substantially the entire surface of the inner coat and a part of the glass bottle surface. PA1 (a) a block copolymer which is either unhydrogenated or selectively hydrogenated to at least some degree and having at least two kinds of polymer blocks wherein one polymer block is designated as A and a second polymer block is designated as B such that prior to hydrogenation, PA1 wherein the aromatic portions of the polymers described in (b)(1), (2), and (3) are at least partially hydrogenated to remove the aromatic character thereof, and PA1 (c) at least one adhesion promoter. PA1 A. preheating a glass container, PA1 B. applying on the external wall surface of the container the powder composition described above, PA1 C. baking the coated container until the powder particles become molten and form a smooth, molten coating on the glass surface, PA1 D. applying to the coated container a synthetic resin selected from the group consisting of epoxy resins, polyurethanes, polycarbonates, polyesters, polystyrenes, ethylene/vinyl acetate copolymers and acrylic homopolymers and copolymers wherein the synthetic resin is applied to substantially the entire surface of the first coating and also to a part of the glass bottle surface, PA1 E. baking the coated container until the synthetic resin forms a smooth coating, and PA1 F. cooling the coated bottle to substantially ambient temperature. PA1 Polystyrene-polybutadiene-polystyrene, PA1 Polystyrene-polyisoprene-polystyrene, PA1 Polystyrene-polybutadiene (polybutadiene-polystyrene)2-5, PA1 Polystyrene-(polyisoprene-polystyrene)2-5, PA1 Polystyrene-poly(ethyl-butadiene)-polystyrene, PA1 Polystyrene-poly(random butadiene-styrene)-polystyrene, PA1 Poly(alpha-methylstyrene)-polybutadiene-poly(alpha-methylstyrene), PA1 Poly(alpha-methylstyrene)-polyisoprene-poly(alpha-methylstyrene), PA1 Poly(styrene-alpha-methylstyrene)-poly(butadiene-isoprene) (styrene-alpha-methylstyrene), and PA1 Poly(vinylxylene)-polybutadiene-poly(vinylxylene). PA1 (1) acrylic monomers other than those cited hereinabove, which monomers generally encompass aryl and reactive esters of acrylic and methacrylic acids, such as phenyl acrylate, phenyl methacrylate, aziridinyl acrylate, glycidyl methacrylate, 2-aminoethyl acrylate, 2-aminopropyl methacrylate, 3-aminopropyl methacrylate, and the like; PA1 (2) ethacrylic and crotonic acids and esters thereof, such as ethyl ethacrylate, methyl crotonate, octyl ethacrylate, heptyl crotonate, octadecyl ethacrylate, cyclohexyl ethacrylate, benzyl crotonate, phenyl ethacrylate, and the like; PA1 (3) amides, alkylol amides, and alkoxyalkyl amides of acrylic, methacrylic, and crotonic acids, wherein the alkyl moieties contain from 1 to about 4 carbon atoms and the alkoxy moiety contains from 1 to about 8 carbon atoms, specific examples being acrylamide, methacrylamide, crotonamide, methylol acrylamide, methoxymethyl methacrylamide, butoxymethyl acrylamide, 2-ethylhexoxymethyl methacrylamide, diacetone acrylamide, and the like; PA1 (4) alpha, beta-ethylenically-unsaturated dicarboxylic acids and anhydrides, such as maleic acid, maleic anhydride, fumaric acid, itaconic acid, mesaconic acid, and the like; PA1 (5) mono- and diesters of alpha, beta-ethylenically-unsaturated dicarboxylic acids, examples of which esters are fumaric acid monoethyl ester, dimethyl itaconate, dipropyl mesaconate, diisopropyl maleate, dicyclohexyl maleate, maleic acid mono (beta-hydroxyethyl) esters, and the like; PA1 (6) alpha, beta-ethylenically-unsaturated nitriles, such as acrylonitrile, methacrylonitrile, ethacrylonitrile, crotonic nitrile, and the like; PA1 (7) vinyl aromatic compounds, such as styrene, vinyltoluene, vinylnaphthalene, chlorostyrene, bromostyrene, and the like; PA1 (8) monounsaturated hydrocarbons, such as ethylene, propylene, and the like; PA1 (9) no more than about 10 weight percent of vinyl esters of alphatic monocarboxylic acids having from 1 to about 18 carbon atoms, such as vinyl acetate, vinyl propionate, vinyl octanoate, vinyl stearate, and the like; and PA1 (10) no more than about 10 weight percent of halogen-containing unsaturated hydrocarbons, such as vinyl chloride, vinyl fluoride, vinylidene chloride, vinylidene fluoride, and the like.
Because of the rather recent concern with environmental considerations, it is especially desirable to be able to apply protective coatings to various substrates such as glass bottles in a non-polluting manner. The use of solid powder particles to coat these substrates eliminates the need for solvent and the accompanying environmental problems. In this connection, see U.S. Pat. No. 3,737,401.
When the powder particles are deposited upon a substrate such as a glass bottle, the particles must be heated to provide a uniform molten coating on the glass bottle. The coating is then cooled to provide a uniform solid coating on the bottle.
When certain thermoplastic elastomers such as styrene/butadiene/styrene block copolymers are used as a major component of the powder particles, the melt flow of the thermoplastic elastomers is not sufficient to provide a uniform molten coating. Although it is known to use copolymers of alphamethylstyrene and styrene with certain elastomers to produce pressure sensitive adhesives and to use such additives in hot melt coatings (see U.S. Pat. No. 3,932,332), the use of this additive does not provide sufficient flow in thermoplastic elastomers at temperatures below that at which the thermoplastic elastomer discolors.
It is also known to use hydrogenated aromatic hydrocarbon petroleum resins as tackifiers for polymers such as styrene/isoprene/styrene block copolymers in a hot melt adhesive. For example, United States Defensive Publication T917008 discloses a hot melt adhesive containing a tackifier which is derived from a polymerized cracked naphtha fraction and having a boiling point between -10.degree. and 280.degree. C. This fraction contains polymerizable unsaturated hydrocarbons, inert paraffins and alkyl benzenes. The polymerizable unsaturated hydrocarbons present in the fraction include aromatic olefins, cyclic olefins, cyclic diolefins, aliphatic olefins and aliphatic diolefins. Of the unsaturated hydrocarbon content, at least about 50% by weight, consists of a mixture of aromatic olefins, cyclic olefins and cyclic diolefins. The aromatic olefins present in the petroleum fraction include styrene, alpha-methylstyrene, vinyl toluene, vinyl xylene, propenyl benzene, indene, methyl indene, ethyl indene, and the like. The cyclic olefins and cyclic diolefins include cyclopentene, cyclopentadiene, dicyclopentadiene, cyclohexene, cyclooctene, and the like. The aliphatic olefins and aliphatic diolefins include butene, butadiene, pentene, pentadiene, octadiene, and the like.
The problem of melt flow of thermoplastic elastomers exists not only with respect to coatings useful for glass bottles but also for other coating applications and for large part molding such as roto casting.
A particularly efficacious method for solving the above-identified problems is disclosed in United States Patent Application Ser. No. 844,963, entitled "Powder Composition and Method of Preparation" and filed concurrently herewith by Martin J. Hannon and Alex S. Forschirm. However, the powder particles produced by this method tend to coalesce and become somewhat tacky, lumpy materials which are somewhat difficult to spray. These powders tend to produce coatings which have the appearance of an orange peel. Since these coatings tend to be rather lumpy, their appearance, adhesive properties and glass fragment retention are not as good as they would be if such lumpiness could be eliminated.
This tendency of thermoplastic elastomers to stick together, coalesce, agglomerate and/or exhibit "blocking," results from an undesired adhesion between touching particles such as occurs under moderate pressure during storage of the particles. Particularly, storage under somewhat elevated temperatures, and under pressures caused by stacking bales or packages of polymer, create conditions favorable for such agglomeration. If the particles of the polymers agglomerate, then it frequently becomes necessary to grind, crush, or otherwise masticate the mass in order to reseparate the particles or to again produce a utilizable particulate material. Such mechanical treatment is burdensome and undesirable because of inconvenience, added labor and time, cost, possible contamination of the elastomer, and possibly in some instances even degradation of some of the polymeric products due to the additional working, temperature, and the like.
In attempting to ease this problem, it is known to apply a dusting agent such as carbon black, talc, zinc stearate, rice flour, chalk, magnesium oxide, infusorial earth, or the like, to the particles in an effort to counteract the natural tackiness or blockiness of the particulate-form polymers. All of these dusting agents, however, have some objectionable characteristics. For example, adding color to the natural polymer may be undesirable for some purposes. The dusting agents may be objectionable for some end uses, such as in clear coatings where the presence of such agents could cause haziness. Silica powder and some grades of talc may possibly pose health hazards under some circumstances that will restrict their use. Stearate powders at levels sufficient to combat tackiness may adversely affect polymer performance properties such as tack, adhesion, optical clarity, and the like.
For a more detailed discussion of the disadvantages of prior art attempts to solve this general problem, see U.S. Pat. Nos. 3,528,841 and 4,027,067 and British specification No. 1,200,532. The disclosure of U.S. Pat. No. 4,027,067 is hereby incorporated by reference.
A particularly efficacious method for solving the agglomeration problem associated with thermoplastic elastomers is disclosed in United States Patent Application Ser. No. 844,812, entitled "Powder Composition and Method of Preparation" and filed concurrently herewith by Martin J. Hannon and Richard K. Green. The disclosure of this patent application is hereby incorporated by reference.
Because of the recent concern over environmental considerations, it is becoming increasingly important to have glass containers which are not only fragment retentive but also returnable, i.e., reusable. Returnable bottles must have coatings which will not substantially degrade, peel off or become substantially less firmly attached to the glass after repeated washings and sterilization procedures.
The search has continued for improved fragment retentive and returnable glass bottles useful in the carbonated beverage and beer industries. This invention was made as a result of that search.